Supporting die



N 8. 1969 E. E. MERRITT ETAL 3,478,390

SUPPORTING DIE Filed Oct. 22, 1965 2 Sheets-Sheet 1 llll H FIE: 1

INVENTORJ fawn/e015. MEKRITT CuRT/s W 771-TERua J'TANLEY E PETERSON A'Rrm/RI B01. 0w 3 fi mddaa 4M G ,47- ToRNEYr United States Patent 3,478,390 SUPPORTING DIE Edward E. Merritt and Curtiss W. Titterud, Anoka, Stanley E. Peterson, Elk River, and Arthur J. Bu-. low, Anoka, Minn., assignors to Federal Cartridge Corporation, Minneapolis, Minn., a corporation of Minnesota Filed Oct. 22, 1965, Ser. No. 502,164 Int. Cl. B29d 23/04 US. Cl. 1814 6 Claims ABSTRACT OF THE DISCLOSURE This invention is an improvement in a machine designed to carry out the process described in the United States Patent 2,961,711, invented by Diedrich et al., issued Nov. 29, 1960 and entitled Process for Strengthening Hollow Bodies of Plastic Material and similar processes for expanding the diameter of thermoplastic materials initially in tube form. It comprises a die block assembly which has a passageway through which the tubing passes. The passageway gradually enlarges from the size of the original tubing to the diameter of the expanded tubing. The first, or supporting, die is aligned with a second, or sizing, die having an inside diameter equal to the desired finished outer diameter of the expanded tubing. These dies are positioned at the end of the heating and tempering bath where the tubing is brought to the desired temperature prior to enlargement and at the precise point where the enlargement of the tubing by internal fluid pressure occurs. The sizing die is partially cooled and the tubing immediately enters a cooling bath upon leaving the sizing die. By means of these two dies in close proximity to each other, the tubing is supported during the expanding process and by positioning the orienting die with relation to the supporting die, tubing wall thickness can be held within closer tolerances than otherwise. The supporting die may be grooved which is believed to hold the tubing against rotation relative to the die which improves the degree of consistency in wall thickness attainable.

Accordingly, it is an object of this invention to provide an improved machine for circumferentially enlarging tubes of thermoplastic olefins and other polymers.

It is a further object of this invention to provide a die for controlling the rate and direction of expansion of a thermoplastic tube having fluid pressure applied internally.

It is another object of this invention to reduce variations in tube wall thickness of tubes of thermoplastic polymers that are being expanded circumferentially by internal fluid pressure.

It is another object of this invention to secure tube material against circumferential movement in either direction, as by rotation or flow of the plastic, or in both directions simultaneously if bi-directional flow occurred, relative to the supporting structure, as the tubing is being expanded radially by internal fluid pressure.

To the accomplishment of the foregoing and related ends, this invention then comprises the features hereinafter fully described and particularly pointed out in the claims, the following description setting forth in detail certain 3,478,390 Patented Nov. 18, 1969 illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principles of the invention may be employed.

The invention will be described with reference to the drawings in which corresponding numerals refer to the same parts and in which:

FIGURE 1 is a longitudinal sectional view of the invention and fragments of the adjacent portions of the machine with which it is used;

FIGURE 2 is an end elevation of the supporting die drawn to an enlarged scale with broken lines representing the continuation of repeated structure;

FIGURE 3 is a sectional View taken on the line and in the direction of the arrow 33 of FIGURE 2;

FIGURE 4 is a fragmentary view of the silhouette of the exit aperture of the supporting die drawn to a larger scale than FIGURES 2 and 3;

FIGURE 5 is a view of the sizing and orienting die used with the supporting die and drawn to the same scale as FIGURE 2; broken lines illustrate continued repeated structure and hidden parts;

FIGURE 6 is a longitudinal sectional view of the structure shown in FIGURE 5 taken on the line and in the direction of the arrows 6-6 of FIGURE 5; it is drawn to the scale of FIGURE 4; and

FIGURE 7 is a fragmentary enlargement of the silhouette of the exit aperture of the sizing and orienting die drawn to a scale twice that of FIGURE 4.

Referring to the drawings and specifically initially to FIGURE 1, the dies of the invention may be seen near the end of the heat exchanger 10, which corresponds to the element designated 4 in FIGURE 3 in the above referred Diedrich et a1. patent. The heat exchanger 10 terminates in a threaded portion 12 which receives a nut 14. The end of the heat exchanger includes a reduced portion 16 against which abutts a grommet 18. The nut 14 has an internal flange or shoulder 20 which engages the other side of grommet 18. As the nut 14 is tightened, the space between shoulder 20 and terminal portion 16 of heat exchanger 10 is reduced. This squeezes grommet 18 which causes it to bulge out into contact with the tube to serve as a temporary seal until the plastic tubing 22 can be engaged by the supporting die 24 in a liquid tight relationship. This is necessary because the tubing 22 is surrounded by the tempering heating solution at a pressure above atmospheric in order to prevent the tube from expanding radially until it is desired to accomplish such expansion.

The die 24 is held in engagement with the heat exchanger by means of a flange 26 being embraced by the hollow nut 28 which threadably engages the threaded end 30 of the nut '14. With the exception of the specific structure of die 24, all the structure described thus far is a commercially available machine that is sold to perform the process of United States Patent 2,961,711

Orienting and sizing die 32 which is secured in a collar structure 34 is adjacent to, but as shown does not abut die 24. Collar structure 34 is frictionally held in frame 36 of a cooling bath structure by suitable means such as the screws 38. The radial position of die 32 relative to die 24 may be controlled and is determined by set screws 40 extending radially through frame collar 36. By loosening clamping screws 38 and turning the set screws 40, the radial position of collar 34 may be altered relative to the stationary die 24 to maintain consistent tube wall thickness. Since the external pressure maintained by the heating tempering fluid in heat exchanger 10 no longer is applied to tube 22 when it reaches supporting die 24, the internal pressure maintained inside of plastic tubing 22 by keeping the left-hand end (not shown) closed and inserting fluid under pressure at the right (not shown) causes tubing 22 to expand radially in close association 3 with the internal diameter of the die 24. Sizing die 32 determines the final outside diameter of tubing 22 as it passes into a cooling area.

Referring now to FIGURE 2, the flange 26 of the supporting die 24 may be seen and also visible is the exit aperture 42 as well as the entrance aperture 44. Also disclosed is the partially ribbed internal surface of the form of supporting die illustrated in FIGURES 2 and 3. The ribs are designated 46 in those two figures.

In FIGURE 3, it can be seen that entrance aperture 44 leads into cylindrical passageway 48. Passageway 48 at 50 begins a gradual enlargement or expansion to exit aperture 42. This expanding portion of the supporting die is defined by a plurality of straight lines as represented by the ribs or grooves 46 in that figure. In the case of the die shown in FIGURE 1, however, where the walls of the enlarging passageway portion of the die are not ribbed, the supporting portion of the die where expansion takes place is in the form of a truncated cone. Die 24 is actually made in two pieces so that a starter tube can be extruded and forced through the machine and the supporting die can later be assembled around the tube. Even a smooth surfaced die otherwise like the one 24 is advantageous, but even greater advantages can be secured by ribbing it. Ribs 46 minimize all rotational movement of the plastic of tube 22, as it passes through supporting die 24. Depth of ribs 46 beyond what is required to so hold the plastic has no advantages and may be undesirable. Accordingly, the depth formation of these ribs might be termed mildly critical within the range of .002 to .008 of an inch in the finished tube. The number of ribs that is used is not critical, and the range that has been used satisfactorily on tubing that is expanded from a diameter of approximately .380 of an inch to a diameter of approximately .790 of an inch is 56 to 120. When smaller tubes, i.e. .650 to .750 of an inch are made, the number of ribs used may be as small as 48.

FIGURE 4 shows a fragment of the exit aperture of die 24 and the range of .002 to .008 of an inch grooves in tubing is the result of .010 to .036 of an inch teeth or ribs measured from the crown of the rib or teeth-like structures there shown to the base thereof at 52.

In FIGURE 5, the sizing die 32 is seen also to have an exit aperture, this one designated 54. A sizing and orienting die may also be provided with ribs as at 56 which will cause the exterior of the tube to be ribbed. Ribbing or grooving has at least one advantage in that a tube of substantially uniform functional characteristics which may have some obvious surface imperfections that cause it to have an undesirable commercial appearance, can be given an appearance to match its functional uniformity. The experience of the inventors assignee has been to use the same number of ribs in the sizing and orienting die as in the case of the supprtoing die. Orienting die 32 also has an entrance aperture which flares outward slightly as at 58 in FIGURE 6 to receive the end of the tubing from the supporting die where the circumferential enlargement of the tube is accomplished. As the tubing is produced continuously during an operating session, after the initial entry of the tube into the sizing orienting die 32, the flare 58 has little function. Tube 22 is momentarily not supported for that brief span. This brief lack of support is not sufiicient to produce any undesirable effects on the finished tubing. In a finished tube, the grooves or ribs, depending on how one views the structure, are of a depth or height of .002 to .008 of an inch. It has been found that .008 of an inch of ribbing is the result when the die is cut, at its deepest, to a depth of from .020 to .036 of an inch measured from the base of a tooth, as at 60 in FIGURE 7, to the crown at 54. A satisfactory pitch between the die teeth is a 40 degree angle in a toothed die having a final mean passageway diameter of .650 to .820 of an inch. The length of the portion of the die that supports the expanding tube may suitably be .950 when the initial tubing has an outside diameter of .385 and a terminal outside diameter of .790. When other sizes of tubing are used, the length may be suitably altered'to produce the desired control of the expanding tube.

Exactly how the support die acts to improve the control of the consistency of tube wall thickness is not known certainly. However, extensive operation of the machine with and without a support die and with and without ribs in the support die has produced the following results. When the machine operates without any support die, wall thickness may vary by as much as .015 of an inch 'or more. When it is considered that, in at least some uses, a wall thickness of from .015 to .025 of an inch wall thickness is commercially required, the variation of .015 of an inch means that much tubing produced without a. support die may be commercially useless. In fact, if the tube ruptures at a very thin spot, operation of the machine is interrupted. When a smooth support die is used, wall thickness variations can be reduced to .008 to .009 of an inch. This decrease in variation lowers substantially the amount of scrap that is produced. Variations can be held to .004 of an inch or less with a ribbed support die in the machine. If a thickness of say .020 of an inch is desirable, virtually all production, once the machine is adjusted and operating smoothly, can be held within the limits of .015 to .025 of an inch.

It is apparent that many modifications and variations of this invention as hereinbefore set forth may be made without departing from the spirit and scope thereof. The specific embodiments described are given by way of example only and the invention is limited only by the terms of the appended claims.

What is claimed is:

1. In a machine that extrudes, crystallizes, reheats and expands by internal fluid pressure polyolefin tubing, the improvement of a supporting die with its axis horizontally positioned for use at the point of expanding the tubing and supporting the same throughout the expanding process comprising a two piece die block each half of which has therein a short section of cylindrical trough-like formation and a longer section of truncated conical trough-like formation; whereby when the two die block pieces are placed together, they form together a die block assembly having a short smooth walled cylindrical passageway and a longer truncated conical passageway having a ribbed surface with the smaller end of the truncated conical passageway matching the cylindrical passageway; said truncated conical passageway generally forming an extension of the cylindrical passageway, said cylindrical passageway having an inside diameter equal to the outside diameter of the initial tubing and the larger end of the conical passageway having the same diameter as the outside of the enlarged tubing.

2. In a machine that extrudes, crystallizes, reheats and expands polyolefin tubing, the improvement of a supporting die with its axis horizontally positioned placed at the point where tubing is expanded in a radial direction by internal fluid pressure in combination with a sizing die, the dies comprising: an apertured assembly having an entrance aperture having the same dimensions as the external dimensions of the original tubing entering the die and having an exit aperture having the dimensions of the tubing after it has been expanded and a connecting passageway within said die forming a gradually expanding supporting surface from said entrance aperture to said exit aperture, said supporting surface being defined by a series of straight lines extending from points near one aperture to corresponding points on the other and being ribbed; and another apertured assembly for sizing and supporting the tubing leaving said exit aperture and being spatially disposed in tubing receiving relationship from said first named apertured assembly.

3. The improvement of claim 1 in which the cylindrical passageway formed by the die block pieces is smooth walled and the truncated conical passageway formed by the die block pieces has its surface ribbed.

4. In a structure for supporting and sizing tubing of thermoplastic olefin that is being expanded by the application of internal fluid pressure the combination of: a supporting die comprising a die assembly having entrance aperture and an exit aperture, a short cylindrical passage- Way extending from said entrance aperture toward but stopping short of said exit aperture and a conical passageway extending from the termination of said cylindrical passageway to said exit aperture, the diameter of said entrance aperture approximating the diameter of the initial tubing and the diameter of the exit aperture being substantially the diameter of the expanded tubing, and a sizing die positioned near the end of the exit aperture of said supporting die, said sizing die comprising a die member having a cylindrical passageway therein, means for supporting said supporting die in a fixed position and means for supporting said sizing die in a variable position relative to said supporting die.

5. The combination of claim 4 in which said sizing die is ribbed and the conical portion of said supporting die is also ribbed and the number of ribs in each of said dies being the same.

6. In a structure for supporting and sizing tubing of thermoplastic olefin that is being expanded by the application of internal fluid pressure the combination of a supporting die comprising a die assembly having entrance aperture and an exit aperture, a short passageway in said die assembly of a configuration and dimension to receive the starting tubing extending from said entrance aperture; a longer passageway extending from the end of said short passageway being of a gradually increasing size from said short passageway to said exit aperture, said passageways being generally circular in cross section, and the surface of said longer passageway being ribbed; the height of said ribs at said exit aperture is in the range of .010 to .036 of an inch, and means for sizing and supporting tubing leaving said exit aperture eccentrically relative to said exit aperture.

References Cited UNITED STATES PATENTS 2,047,554 7/1936 Fischer 18-145 XR 2,086,285 7/ 1937 Putterlik. 2,574,555 11/ 1951 Galloway. 2,987,767 6/1961 Berry et a1. 18145 XR 3,144,494 8/1964 Gerow. 3,182,108 5/1965 Branscum. 3,190,739 6/ 1965 Wilson. 3,311,679 3/ 1967 Moore. 3,346,920 10/ 1967 Fields 18-145 3,212,132 10/ 1965 Westlake. 2,716,777 9/ 1955 Hagen.

FOREIGN PATENTS 986,585 1951 France.

WILLIAM J. STEPHENSON, Primary Examiner U.S. c1. X.R, 

